Furnaces



Oct. 6, 1959 U. o; BL5M m 2,907,288

FURNACES Filed Sept. 14. 1953.

United States Patent FURNACES Uno Olof Blomquist, Vasteras, Sweden, assignor to AB SvenskaMaskinverken, Sodertalje, Sweden, a corpora- 7 This invention relates to a furnace for the combustion of powdered or small-size solid fuel and also for liquid or gaseous fuels alone or in combination with solid fuels.

In modern longitudinaly extended furnaces of common type for steam boilers or the like, the mode and rate of combustion are substantially dependent upon the differences in temperature occurring in the furnace and the thermal gas flow caused by said temperature differences. Accordingly, combustion will substantially take place in the central portion of the furnace, while the surrounding portion is poorly utilized, resulting in a low average rate of combustion. In order to increase the rate of combustion, it has become common practice to induce a revolving motion tothe mass of gases, for instance by the use of tangentially directed burners placed in the corners of the furnace, the result being, however, not very satisfactory. In addition, it is difficult in steam boilers of usual construction to maintain constant the temperature of superheat of the steam at greatly varying steam generation. Further, it is not possible to vary to a noticeable degree the conditions of combustion with regard to the properties of different fuels.

It is the object of this invention to eliminate the above inconveniencies. The furnace according to the invention comprises a longitudinally extended combustion chamber having a plurality of means for the supply of crushed or finely divided fuel and combustion air, said means being arranged to impart to the fuel and combus tion air a substantially helical movement around an imaginary axis, the main axis of the combustion chamber, and a gas outlet opening the cross sectional area of which is considerably smaller than the cross sectional area of the combustion chamber which downwardly merges into a trough-shaped shaft. In a preferred embodiment of the invention, an auxiliary furnace having a grate for separate combustion is provided below the trough-shaped shaft and in open communication therewith. This grate may be a longitudinally extended moving grate or a circular grate. In large furnaces and particularly in vertical furnaces, it may be suitable to provide a plurality of minor grates. Especially in furnaces having a vertical main axis the arrangement according to the invention permits of controlling the course of combustion by external means so as to vary the posi tion of the combustion zone in a vertical direction in spite of the thermal gas flow, this possibility being important with regard to varying properties of the fuel. In connection with steam boilers it is highly desirable to have the possibility of controlling the fiue gas temperature at the outlet of the combustion chamber such as to maintain constant the steam temperature at varying rates of steam generation.

The control of the course of combustion by external means is efiected by a certain location and shape of the air inlet openings. Preferably some of the air inlet openings are located in the upper portion of the combustion chamber and other openings are located in the lower portion, at least part of these openings being directed tangentially to the combustion chamber. Between the upper and lower air inlet openings and/or at the same level as these openings, there are provided means for the supply of fuel. The supply conduits for the upper and lowerair inlet openings may-be combined with each other and provided-with an air distributing device to vary the proportion between 'thetwo'main air streams supplied to the combustion chamber. The furnace may communicate with a reheater into which a small amount of combustion air may be supplied in a suitable manner, or directly with heat absorption surfaces.

Referring to the drawings:

Figure 1 is a vertical sectional view of the invention.

Figure 2 is a transverse sectional view of the form shown in Figure 1.

Referring to the drawing, numeral 1 denotes the wall of a combustion chamber which is entirely or partly covered on the inside with tubes 2 for a fluid, such as circulating water, for generating steam or hot water. The tubes may communicate with a steam dome 3-provided above the combustion chamber.

According to Figs. 1 and 2, the furnace 1 has a circular or annular grate 32, resulting in a more symmetrical arrangement of the entire furnace.

Primary combustion air is supplied in the usual manner from below through the above described grates of the furnace which acts to stabilize the combustion in the combustion chamber.

The constricted outlet opening 19 according to Figs. 1 and 2 communicates with a reheater 34 in which complete combustion may be carried out. To this end, tangentially directed air supply conduits 35 communicate with the reheater immediately above the outlet opening of the combustion chamber. The air supply conduit 35 is connected to a supply system for the upper and lower part of the combustion chamber. By means of the distributor 26, the air is divided into two main streams the upper one of which is partly admitted into the reheater 34. By means of flap valves 36 and 37, the proportion between the air quantities entering through the conduits 24 and 35 may be varied in accordance with requirements. Alternatively, air may be separately supplied to the reheater 34.

The invention may be used to improve existing radiation type furnaces. To this end, the outlets 19 and the constricting members may be constructed as a supplementary structure including water-cooled boiler tubes, and openings may be provided.

What I claim is: v

A furnace for steam boilers and the like comprising an elongated combustion chamber for burning finely divided fuel and intended to operate at so low temperatures that the mineral constituents in the ash will substantially not melt, a radiant chamber above said combustion chamber, said combustion chamber having at its upper end a gas outlet opening communicating with said radiant chamber and located substantially centrally thereof, boiler fluid tubes positioned adjacent the walls of said combustion chamber, a steam drum above said radiant chamber and communicating with said tubes, means for supplying finely divided fuel into said combustion chamber, a plurality of means located at different planes transverse to the longitudinal axis of said combustion chamber for introducing combustion air into said combustion chamber, said fuel and combustion air being introduced tangentially into the combustion chamber so as to impart to the fuel and combustion air a substantially helical movement around said longitudinal axis, said gas outlet opening having a depending rim extending into said combustion chamber, said furnace hav- 3 ing a tubular distributor provided with an upper branch and a'lower branch for introducing combustion airta'ngentially into the combustion chamber, one of said branches communicating with said radiant chamber above said gas outlet. 5

:ReferencesCitedin thcfile of this patent UNITED STATES PATENTS 901,232 Eldred- 'Oct. 13, 1908 1,091,475 Best Mar. '31, 1914 10 1,918,397 Jezler July 18, 1933 '4 1 Kerr et a1. Sept. 5, 1944 Lemaire Aug. 16, 1949 Glaeser Oct. 4, 1949 Kreisinger Nov. 6, 1951 Birkner Jan. 17, 1956 Hubel May 28, 1957 FOREIGN PATENTS Great Britain Mar. 22, 1923 Great Britain Dec. :11, 1928 

